Microphone device with single crystal piezoelectric film and method of forming the same

ABSTRACT

A method of forming a microphone device includes: forming a through-hole in a substrate wafer; providing a second wafer; bonding the second wafer to the substrate wafer; and forming a top electrode over a first surface of a single-crystal piezoelectric film of the second wafer. The second wafer may include the single-crystal piezoelectric film. The single-crystal piezoelectric film may have a first surface and an opposing second surface. The second wafer may further include a bottom electrode arranged adjacent to the second surface, and a support member over the single-crystal piezoelectric film. The through-hole in substrate wafer may be at least substantially aligned with at least one of the top electrode and the bottom electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 16/722,143,filed on Dec. 20, 2019. The content of the application is incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Various embodiments relate to microphone devices and methods of forminga microphone device.

2. Description of the Prior Art

Existing microphone devices manufactured using semiconductor technologytypically suffers from yield loss caused by stress mismatches within thepiezoelectric material. To compensate for the stress mismatch, somemicrophone devices include two layers of piezoelectric layers withopposing stress distribution. However, it is challenging to achieveconsistency in the performance of such microphone devices, as thepiezoelectric layer in different devices may bend differently due topoor stress uniformity in the piezoelectric layers, causing thedimensions of the air gaps in the microphone devices to vary.

SUMMARY OF THE INVENTION

According to various embodiments, there may be provided a microphonedevice. The microphone device may include: a substrate wafer, a supportmember bonded to a front surface of the substrate wafer, asingle-crystal piezoelectric film provided over the support member, atop electrode and a bottom electrode. The single-crystal piezoelectricfilm may have a first surface and an opposing second surface. The topelectrode may be arranged adjacent to the first surface of thesingle-crystal piezoelectric film. The bottom electrode may be arrangedadjacent to the second surface of the single-crystal piezoelectric film.The substrate wafer may have a through-hole formed therein. Thethrough-hole of the substrate wafer may be at least substantiallyaligned with at least one of the top electrode and the bottom electrode.

According to various embodiments, there may be provided a method offorming a microphone device. The method may include: forming athrough-hole in a substrate wafer; providing a second wafer; bonding thesecond wafer to the substrate wafer; and forming a top electrode over afirst surface of a single-crystal piezoelectric film of the secondwafer. The second wafer may include the single-crystal piezoelectricfilm. The single-crystal piezoelectric film may have a first surface andan opposing second surface. The second wafer may further include abottom electrode arranged adjacent to the second surface, and a supportmember over the single-crystal piezoelectric film. The through-hole insubstrate wafer may be at least substantially aligned with at least oneof the top electrode and the bottom electrode.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments are described with reference to the following drawings, inwhich:

FIGS. 1A to 1N show a method of forming a microphone device according tovarious non-limiting embodiments.

FIG. 2 shows a top view of the microphone device of FIG. 1N.

FIG. 3 shows a process, as well as a cross-sectional view of amicrophone device according to various non-limiting embodiments.

FIG. 4 shows a cross-sectional view of a microphone device according tovarious non-limiting embodiments.

FIG. 5 shows a flow diagram of a method for forming a microphone deviceaccording to various non-limiting embodiments.

DETAILED DESCRIPTION

Embodiments described below in context of the devices are analogouslyvalid for the respective methods, and vice versa. Furthermore, it willbe understood that the embodiments described below may be combined, forexample, a part of one embodiment may be combined with a part of anotherembodiment.

It will be understood that any property described herein for a specificdevice may also hold for any device described herein. It will beunderstood that any property described herein for a specific method mayalso hold for any method described herein. Furthermore, it will beunderstood that for any device or method described herein, notnecessarily all the components or steps described must be enclosed inthe device or method, but only some (but not all) components or stepsmay be enclosed.

In order that the invention may be readily understood and put intopractical effect, various embodiments will now be described by way ofexamples and not limitations, and with reference to the figures.

According to various non-limiting embodiments, a microphone device mayinclude a thin film of single-crystal piezoelectric material bonded to aComplementary Metal-Oxide-Semiconductor (CMOS) wafer or other types ofactive substrates. The microphone device may include a top electrode anda bottom electrode patterned onto opposing sides of the thin film ofsingle-crystal piezoelectric material. A single-crystal piezoelectricfilm, as compared to polycrystalline piezoelectric material deposited byphysical vapor deposition (PVD), has the advantage of having no internalstresses. It is thus possible to achieve uniformity of stressdistribution, and to obtain consistent performance in the microphonedevice. Single-crystal piezoelectric film may exhibit the desirablepiezoelectric properties that might be offered by a polycrystallineceramic element if all of its domains were perfectly aligned. Suitablematerials for the single-crystal piezoelectric film may include aluminumnitride (AlN), scandium aluminum nitride (ScAlN), lead magnesiumniobate-lead titanate (PMN-PT), lead zirconate niobate-lead titanate(PZN-PT), lithium niobate (LiNbO₃), lithium tetraborate (Li₂B₄O₇),quartz and barium titanate (BaTiO₃).

The starting material for fabricating the microphone device may be apiezoelectric-on-insulator (POI) wafer with tight thickness control anduniformity. Using the POI wafer as a starting material may allow thethin film of piezoelectric material to be transferred onto anothersubstrate, such as a CMOS wafer, before the device features arefabricated onto the piezoelectric material. The quality of the thin filmmay be also be maintained even when the thickness is reduced.

FIGS. 1A to 1N show a method of forming a microphone device 102according to various non-limiting embodiments. FIG. 1A shows a process100A. In the process 100A, a piezoelectric-on-insulator (POI) wafer 110may be provided. The POI wafer 110 may include a piezoelectric layer112, an insulator layer 114 and a substrate layer 116. The piezoelectriclayer 112 may include a single piezoelectric crystal. The insulatorlayer 114 may serve to electrically insulate the piezoelectric layer 112from the substrate layer 116. The insulator layer 114 may include anoxide, such as silicon dioxide. The substrate layer 116 may include asemiconductor material, such as silicon. Other types of materialcomposition for the insulator layer 114 and the substrate layer 116 areacceptable, as these two layers will be subsequently removed.

FIG. 1B shows a process 100B. In the process 100B, a bottom electrode120 may be formed. The process 100B may also include forming a bottompassivation layer 122. The electrode and passivation layer will be on abottom surface of the piezoelectric layer 112 when the POI wafer 110 isflipped around and bonded to another wafer. Forming the bottom electrode120 may include depositing a metal layer onto the piezoelectric layer112, then patterning the metal layer using a first mask to form thebottom electrode 120. The metal layer may include molybdenum. Formingthe bottom passivation layer 122 may include depositing a layer ofetch-resistant material. The etch-resistant material may be resistant toetching by an etchant for silicon, such as sulfur hexafluoride (SF₆).The etch-resistant material may include aluminum nitride (AlN), aluminumoxide (Al₂O₃), or combinations thereof.

FIG. 1C shows a process 100C. The process 100C may include formingstand-off structures, also referred herein as support members 130.Forming the support members 130 may include depositing a support layeronto the bottom passivation layer 122. The process 100C may furtherinclude depositing a barrier material (not shown in the figure) over thesupport layer, before depositing a first bonding metal 132 over thesupport layer. The barrier material may prevent eutectic reaction ormixing of the support members 130 with the first bonding metal 132. Thebarrier material may include titanium. The first bonding metal 132 mayinclude germanium (Ge). The support layer, the barrier material and thefirst bonding metal 132 may be etched using a second mask. The etchingprocess may be carried out using an etchant which does not react withthe bottom passivation layer 122. For example, the etchant may includeSF₆. The bottom passivation layer 122 may protect the bottom electrode120 from being etched away, during the formation of the support members130. A suitable material for the support layer may be, for example,silicon. In embodiments where the support members are formed of silicon,the support members 130 may also be referred to as silicon pillars. Theetching process may include deep reactive-ion etching (DRIE), which is ahighly anisotropic etch process, so as to create steep side walls on thesupport members 130. The DRIE process may offer precise control of ±0.1°over the angle of side walls of the support members 130, as well asprecise control over dimensions of ±50 nm. The side walls of the supportmembers 130 may be at least substantially vertical. The side walls ofthe support members 130 may be at least substantially perpendicular, forexample, 90°±0.1°, relative to the POI wafer 110 and also at leastsubstantially perpendicular to a substrate wafer 140 that it issubsequently bonded to. After the etching process, a plurality ofsupport members 130 coated with the barrier material and the firstbonding metal 132 may remain. These support members 130 may subsequentlyserve to support a vibration member which includes the bottom electrode120, a top electrode and a region of the piezoelectric layer 112 thatlies between the bottom electrode 120 and the top electrode. As such,the support members 130 may be arranged laterally offset from the bottomelectrode 120 so as not to obstruct movements of the vibration member.The dimension of the lateral offset may define device criticalparameters, such as vibrating frequency range and quality factor. Inother words, the dimension of the lateral offset may be selected to meetthe desired characteristics of the microphone device.

FIG. 1D shows a process 100D. The process 100D may include providing asubstrate wafer 140, flipping the POI wafer 110 from the process 100Cand arranging the flipped POI wafer 110 over the substrate 140 as shown.The substrate wafer 140 may be a CMOS wafer, or may be a bare siliconwafer, or may be any other types of suitable wafers. A second bondingmetal 142 may be deposited onto the substrate wafer 140. The secondbonding metal 142 may be patterned to align with the first bonding metal132 when the POI wafer 110 is flipped onto the substrate wafer 140. Thesecond bonding metal 142 may include a metal that may form a eutecticalloy with the first bonding metal 132. For example, the second bondingmetal 142 may include aluminum (Al) which may form an alloy with the Gein the first bonding metal 132. By this process, the device that iseventually fabricated in the POI wafer 110 may be integrated with a CMOSwafer or other types of external circuit housed in the substrate wafer140, without the extra cost related to system in package (SiP)approaches.

FIG. 1E shows a process 100E. The process 100E may include bonding thePOI wafer 110 to the substrate wafer shown in process 100D. Eutecticbonding of the first bonding metal 132 to the second bonding metal 142may form a bonding layer 150. The bonding process may take place ataround 450 degrees Celsius. The bonding layer 150 may include an alloyof the first bonding metal 132 and the second bonding metal 142, such asAl/Ge. Part of the second bonding metal 142 may remain uncombined withthe first bonding metal 132, and may subsequently form part of aninterconnect layer.

FIG. 1F shows a process 100F. The process 100F may include removing theinsulator layer 114 and the substrate layer 116 of the POI wafer 110,such that only the piezoelectric layer 112 of the initial POI wafer 110remains. The substrate layer 116 may first be removed by a combinationof grinding and etching. Next, the now exposed insulator layer 114 maybe removed by etching, for example, using vapor hydrofluoric acid (VHF)etching or wet etching. The piezoelectric layer 112 may be furthergrinded or etched to reduce the thickness of the piezoelectric layer112. The piezoelectric layer 112, or the reduced thickness piezoelectriclayer, may be referred hereafter as a piezoelectric film 160.

FIG. 1G shows a process 100G. The process 100G may include forming a topelectrode 162 on the piezoelectric film 160. Forming the top electrode162 may including depositing a metal layer over the piezoelectric film160 and then patterning the deposited metal layer using a third mask,similar to the process of forming the bottom electrode 120. The process100G may also include forming a top passivation layer 164. The processof forming the top passivation layer 164 may be similar to the processof forming the bottom passivation layer 122. The top electrode 162 mayhave the same material composition as the bottom electrode 120. The toppassivation layer 164 may have the same material composition as thebottom passivation layer 122. In the same process as forming the topelectrode 162, a top electrical pad 168 may be formed using the thirdmask. The top electrical pad 168 may be connected to the top electrode162 and may serve as an electrical contact point for external devices toconnect to the top electrode 162.

FIG. 1H shows a process 100H. The process 100H may include adding anetch buffer layer 170. The etch buffer layer 170 may include adielectric material, for example silicon dioxide. The process 100H mayfurther include etching a region of the etch buffer layer 170 and thetop passivation layer 164 that overlaps with the top electrical pad 168using a fourth mask, so as to expose a top surface of the top electricalpad 168. The etch buffer layer 170 may prevent the top passivation layer164 from being etched in the process 100K, as will be described withrespect to FIG. 1K.

FIG. 1I shows a process 100I. The process 100I may include forming afirst via 180 that reaches the bottom electrode 120. The process 100Imay also include forming a second via 182 that reaches one of thesupport members 130. Forming the first via 180 and the second via 182may include etching the etch buffer layer 170, the top passivation layer164, the piezoelectric film 160, and the bottom passivation layer 122,using a fifth mask.

FIG. 1J shows a process 100J. The process 100J may include deepening thesecond via 182 so that it reaches to the bonding layer 150. Deepeningthe second via 182 may include etching the silicon pillar 130 under thesecond via 182, using a sixth mask.

FIG. 1K shows a process 100K. The process 100K may include forming aninterconnect member 190. Forming the interconnect member 190 may includedepositing an electrical conductor material over the semiconductordevice from the process 100I and then etching the electrical conductormaterial using a seventh mask. The electrical conductor material mayhave the same material composition as the bonding layer 150. Theinterconnect member 190 may extend into the first via 180 and the secondvia 182, and may line the sidewalls of the vias. The etch buffer layer170 may protect the top passivation layer 164 from being etched duringthe process of etching the electrical conductor material to form theinterconnect member 190. In other words, the etch buffer layer 170 mayserve as a sacrificial layer for the process of etching the electricalconductor material to form the interconnect member 190.

FIG. 1L shows a process 100L. The process 100L may include removing theetch buffer layer 170, for example, by using an etchant.

FIG. 1M shows a process 100M. The process 100M may include forming arelease slit 192, which may be a through-hole in the piezoelectric film160. The release slit 192 may be laterally offset from each of the topelectrode 162 and the bottom electrode 120. The release slit 192 may beformed through an entire thickness of the piezoelectric film 160, andmay extend from the top passivation layer 164 to the bottom passivationlayer 122. The process 100M may include etching the piezoelectric film160 using an eight mask. Forming the release slit 192 may includeetching the piezoelectric film 160, as well as the top passivation layer164 and the bottom passivation layer 122. The process of forming therelease slit 192 may forma cantilever member 194 in the piezoelectricfilm 160. The release slit 192 may separate an active region 204 of thepiezoelectric film 160 from the rest of the piezoelectric film 160. Theactive region 204 may at least partially overlap with at least one ofthe top electrode 162 and the bottom electrode 120. The cantilevermember 194 may include the active region 204. The cantilever member 194has a free end located beside the release slit 192, which may bedisplaceable out of a plane of the piezoelectric film 160. Thecantilever member 194 may have an anchored end that may be restrainedfrom being displaced out of the plane of the piezoelectric film 160. Theanchored end may be fixed on the substrate wafer 140 by one of thesupport members 130.

FIG. 1N shows a process 100N. The process 100N may include forming athrough-hole 202 in the substrate wafer 140. Forming the through-hole202 may include etching the device obtained from the process 100M at thebackside of the device. The through-hole 202 may be at leastsubstantially aligned with at least one of the top electrode 162 and thebottom electrode 120. In other words, the through-hole 202 may be atleast substantially aligned with the active region 204.

FIG. 2 shows a top view 200 of the microphone device 102 according tovarious non-limiting embodiments. FIG. 1N also shows a cross-sectionalview of the microphone device 102 when the microphone device 102 is cutalong the line AA′. The microphone device 102 may include a transducer.The microphone device 102 may include an active region 204 and a contactregion 206. The active region 204 may include the top electrode 162, thebottom electrode 120 and a portion of the piezoelectric film 160arranged between these electrodes. The contact region 206 may includethe interconnect member 190, the top electrical pad 168, a region of thebonding layer 150 underlying the second via 182, and a region of thesecond bonding metal 142 underlying the second via 182. The supportmembers 130 may support the piezoelectric film 160 over a cavity 105between the piezoelectric film 160 and the substrate wafer 140. Thesupport members may provide a precise boundary for the resonator region104. The support member may be formed out of silicon, thereby allowingprecise angles to be etched. There may be one or more air gaps 108between every two adjacent support members 130. The air gaps 108 areempty spaces that electrically insulate the adjacent support members130. Airflow, which may include acoustic waves, may enter the microphonedevice 102 via the through-hole 202, to come into contact with theactive region 204. Acoustic waves may enter the microphone device 102and cause the cantilever member 194 to vibrate out-of-plane. Thepiezoelectric film 160 may convert vibrations in the active region 204,i.e. an acoustic signal, into electrical signals. The top electrode 162and the bottom electrode 120 may carry the electrical signals to thecontact region 206 by electrical conduction. The electrical signals thatare indicative of the acoustic signal, may be output from the microphonedevice 102 through the contact region 206.

FIG. 3 shows a process 300, as well as a cross-sectional view of amicrophone device 302 according to various non-limiting embodiments. Theprocess 300 may include depositing a dielectric layer 308 over themicrophone device 102. The dielectric layer 308 may be deposited bychemical vapor deposition (CVD). The dielectric layer 308 may beprovided above the piezoelectric film 160, for example, adjacent to thetop passivation layer 164. Alternatively, or additionally, thedielectric layer 308 may be provided under the piezoelectric film 160,for example, adjacent to the bottom passivation layer 122. Thedielectric layer 308 may include at least one of silicon oxide, siliconnitride or other dielectric materials. Following the deposition of thedielectric layer 308, the dielectric layer 308 may be etched, so as toprovide access to the contact region 206. The dielectric layer 308 maydistribute stress exerted on it at least substantially uniformly. Assuch, the dielectric layer 308 may pull the neutral axis of thecantilever member 194 out of the piezoelectric film 160, therebyimproving the ability of the cantilever member 194 to transduce acousticsignals to electrical signals. Consequently, the microphone device 302may have an improved performance as compared to the microphone device102. FIG. 4 shows a cross-sectional view 400 of a microphone device 402according to various non-limiting embodiments. The microphone device 402may be similar to the microphone device 102 but may differ from themicrophone device 102 in that it has a bimorph cantilever member 494. Inother words, the microphone device 402 may include two piezoelectricfilms, 160 and 460. The microphone device 402 may include anintermediate electrode layer 412 that lies between the piezoelectricfilm 160 and the further piezoelectric film 460. The top electrode 162may be arranged adjacent to, and above, the further piezoelectric film460. The bottom electrode 120 may be arranged adjacent to, and below,the piezoelectric film 160. The interconnect may include an electricalconnection to the intermediate electrode layer 412.

According to various non-limiting embodiments, a microphone device maybe provided. The microphone device may be any one of the microphonedevices 102, 302 and 402. The microphone device may include a substratewafer, such as the substrate wafer 140. The substrate wafer may have athrough-hole 202 formed therein. The microphone device may include asupport member, for example, the support member 130. The support membermay be bonded to a front surface of the substrate wafer. The microphonedevice may include a single-crystal piezoelectric film, such as thepiezoelectric film 160 or the piezoelectric layer 112. Thesingle-crystal piezoelectric film may have a first surface and anopposing second surface. The single-crystal piezoelectric film may beprovided over the support member. The microphone device may include atop electrode arranged adjacent to the first surface of thesingle-crystal piezoelectric film, and a bottom electrode arrangedadjacent to the second surface of the single-crystal piezoelectric film.The top electrode may be the top electrode 162. The bottom electrode maybe the bottom electrode 120. The through-hole 202 of the substrate wafermay be at least substantially aligned with at least one of the topelectrode and the bottom electrode. The piezoelectric film may have arelease slit, such as the release slit 192 formed therein, such thatpart of the piezoelectric film may form a cantilever member. Thecantilever member may be the cantilever member 194. The cantilevermember 194 may have a moveable end that may vibrate out of a plane ofthe piezoelectric film when acoustic waves are received through thethrough-hole of the substrate wafer.

According to various non-limiting embodiments, the microphone device mayinclude a further single-crystal piezoelectric film provided over atleast a portion of the top electrode, and a further electrode arrangedover the further single-crystal piezoelectric film. The furthersingle-crystal piezoelectric film may be the piezoelectric film 460. Inthis embodiment, the top electrode may be the intermediate electrodelayer 412, and the further electrode may be the top electrode 162. Thetop electrode may at least substantially cover the first surface of thesingle-crystal piezoelectric film. The further single-crystalpiezoelectric film may have the same dimensions as the single-crystalpiezoelectric film. The further single-crystal piezoelectric film may beidentical in composition, as the single-crystal piezoelectric film.

According to various non-limiting embodiments, the support member mayinclude a plurality of silicon pillars. Each silicon pillar may haveside walls that are perpendicular to the front surface of the substratewafer. Each silicon pillar may be electrically isolated from adjacentsupport members by one or more air gaps.

According to various non-limiting embodiments, the microphone device mayfurther include a bonding layer provided over at least part of the frontsurface of the substrate wafer. The support member may be bonded to thesubstrate wafer by the bonding layer. The bonding layer may include thebonding layer 150. The bonding layer may additionally include the secondbonding metal 142. The bonding layer may include at least one ofaluminum, germanium, or combinations thereof.

According to various non-limiting embodiments, the microphone device mayfurther include a top passivation layer arranged adjacent to the firstsurface of the single-crystal piezoelectric film and enclosing the topelectrode therein, and a bottom passivation layer arranged adjacent tothe second surface of the single-crystal piezoelectric film andenclosing the bottom electrode therein. The top passivation layer mayinclude the top passivation layer 164. The bottom passivation layer mayinclude the bottom passivation layer 122. Each of the top passivationlayer and the bottom passivation layer may include a material that isresistant to etching by SF₆. The microphone device may further includean interconnect member at least partially arranged over the firstsurface of the single-crystal piezoelectric film and extending downthrough a via in the single-crystal piezoelectric film to reaching thebonding layer. The interconnect member may be the interconnect member190. The interconnect member and the bonding layer may include the samematerial composition.

According to various non-limiting embodiments, the microphone device mayfurther include a dielectric layer provided adjacent to thesingle-crystal piezoelectric film. The dielectric layer may include thedielectric layer 308. The second surface of the single-crystalpiezoelectric film may face the front surface of the substrate wafer.The dielectric layer may be adjacent to the first surface of thesingle-crystal piezoelectric film. Alternatively, the dielectric layermay be adjacent to the second surface of the single-crystalpiezoelectric film.

According to various non-limiting embodiments, each of the top electrodeand the bottom electrode includes a plurality of finger members. Theplurality of finger members of the top electrode may at leastsubstantially overlap with the plurality of finger members of the bottomelectrode.

According to various non-limiting embodiments, at least one of the topelectrode and the bottom electrode may include segments of differentthicknesses.

According to various non-limiting embodiments, the single-crystalpiezoelectric film may include segments of different thicknesses.

FIG. 5 shows a flow diagram 500 of a method for forming a microphonedevice according to various non-limiting embodiments. The microphonedevice may be any one of the microphone devices 102, 302 and 402. Themethod may include forming a through-hole 202 in a substrate wafer, in502. 502 may include the process 100N. The substrate wafer may be thesubstrate wafer 140. The method may include providing a second wafer, in504. The second wafer may include a single-crystal piezoelectric filmhaving a first surface and an opposing second surface, a bottomelectrode arranged adjacent to the second surface of the single-crystalpiezoelectric film, and a support member arranged over the secondsurface of the single-crystal piezoelectric film. The single-crystalpiezoelectric film may include the piezoelectric film 160 or thepiezoelectric layer 112. The support member may include the supportmembers 130. The bottom electrode may be the bottom electrode 120. 504may include the processes 100A to 100C. The method may include bondingthe second wafer to the substrate wafer, in 506. 506 may include theprocess 100E. The method may include forming a top electrode over thefirst surface of the single-crystal piezoelectric film, in 508. The topelectrode may be the top electrode 162. The through-hole 202 in thesubstrate wafer may be at least substantially aligned with at least oneof the top electrode and the bottom electrode.

According to various non-limiting embodiments, providing the secondwafer in 504, may include providing a POI wafer, like in the process100A. The POI wafer may be the POI wafer 110. The POI wafer may includethe single-crystal piezoelectric film, an insulator layer and asubstrate layer. Providing the second wafer may further includedepositing a first metal layer on the second surface of thesingle-crystal piezoelectric film, and patterning the first metal layerto form the bottom electrode, like in the process 100B. Providing thesecond wafer may further include forming the support member over thesecond surface of the single-crystal piezoelectric film, like in theprocess 100C. Forming the support member may include depositing siliconover the second surface of the single-crystal piezoelectric film, andpatterning the deposited silicon to form a plurality of silicon pillars.

According to various non-limiting embodiments, in 508, providing the topelectrode may include removing the insulator layer and the substratelayer after the second wafer is bonded to the substrate wafer, like inthe process 100F. Removal of the insulator layer and the substrate layermay expose the first surface of the single-crystal piezoelectric film.Providing the top electrode may include depositing a second metal layeron the first surface of the single-crystal piezoelectric film, andpatterning the second metal layer to form the top electrode.

According to various non-limiting embodiments, the method may furtherinclude providing a first passivation layer over the first surface ofthe single-crystal piezoelectric film and the top electrode to enclosethe top electrode. The method may further include providing a secondpassivation layer over the second surface of the single-crystalpiezoelectric film and the bottom electrode to enclose the bottomelectrode.

According to various non-limiting embodiments, the second wafer mayfurther include a further single-crystal piezoelectric film stacked overthe single-crystal piezoelectric film, and a middle electrode providedbetween the single-crystal piezoelectric film and the furthersingle-crystal piezoelectric film. The middle electrode may include theintermediate electrode layer 412.

According to various non-limiting embodiments, the method may furtherinclude providing a dielectric layer over the single-crystalpiezoelectric film. Providing the dielectric layer may includedepositing the dielectric material by CVD.

While embodiments of the invention have been particularly shown anddescribed with reference to specific embodiments, it should beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims. The scope of theinvention is thus indicated by the appended claims and all changes whichcome within the meaning and range of equivalency of the claims aretherefore intended to be embraced. It will be appreciated that commonnumerals, used in the relevant drawings, refer to components that servea similar or the same purpose.

It will be appreciated to a person skilled in the art that theterminology used herein is for the purpose of describing variousembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method of forming a microphone device, themethod comprising: forming a through-hole in a substrate wafer;providing a second wafer, wherein the second wafer comprises asingle-crystal piezoelectric film having a first surface and an opposingsecond surface, a bottom electrode arranged adjacent to the secondsurface, and a support member over the single-crystal piezoelectricfilm; bonding the second wafer to the substrate wafer; and forming a topelectrode over the first surface of the single-crystal piezoelectricfilm; wherein the through-hole in the substrate wafer is at leastsubstantially aligned with at least one of the top electrode and thebottom electrode.
 2. The method of claim 1, wherein the second waferfurther comprises: a further single-crystal piezoelectric film stackedover the single-crystal piezoelectric film; and a middle electrodeprovided between the single-crystal piezoelectric film and the furthersingle-crystal piezoelectric film.
 3. The method of claim 1, whereinproviding the second wafer comprises: providing apiezoelectric-on-insulator wafer comprising the single-crystalpiezoelectric film, an insulator layer, and a substrate layer;depositing a first metal layer on the second surface of thesingle-crystal piezoelectric film; patterning the first metal layer toform the bottom electrode; and forming the support member over thesecond surface of the single-crystal piezoelectric film.
 4. The methodof claim 3, wherein providing the top electrode comprises: removing theinsulator layer and the substrate layer after the second wafer is bondedto the substrate wafer, to expose the first surface of thesingle-crystal piezoelectric film; depositing a second metal layer onthe first surface of the single-crystal piezoelectric film; andpatterning the second metal layer to form the top electrode.
 5. Themethod of claim 3, wherein forming the support member comprises:depositing silicon over the second surface of the single-crystalpiezoelectric film, and patterning the deposited silicon to form aplurality of silicon pillars.
 6. The method of claim 1, furthercomprising: providing a first passivation layer over the first surfaceof the single-crystal piezoelectric film and the top electrode toenclose the top electrode.
 7. The method of claim 6, further comprising:providing a second passivation layer over the second surface of thesingle-crystal piezoelectric film and the bottom electrode to enclosethe bottom electrode.
 8. The method of claim 1, further comprising:providing a dielectric layer over the single-crystal piezoelectric film.